The present invention relates generally to safety systems at work sites, and in particular to personal alarm devices (PADs) for use with an interactive magnetic marker field and proximity warning system. Many methods have been devised to protect people from being struck, pinched, crushed or otherwise harmed by vehicles and mobile equipment. Such vehicles and mobile equipment may be used for above and below ground operations. Examples of the equipment include: road construction equipment such as trucks, road graders, rollers and pavers; surface mining equipment, such as for use with gravel and sand operations, front end loaders, trucks, dozers, conveyors and other items; underground mining equipment such as continuous miners, shuttle cars, conveyors, crushers, load-haul-dump vehicles, man-trips, tractors, and other items. The equipment also includes fork lifts, cranes, and trucks used at warehouses and shipping ports.
The invention is particularly applicable to work sites that require personnel to be in close proximity to various hazardous elements, such as machines, mobile equipment, remotely controlled machines, and operated vehicles. Such work environments may include locations that are inherently dangerous and should be avoided or entered only with great caution. Examples of such work environments are surface mining, underground mining, sand and gravel operations, road construction, warehouses, shipping docks, coke plants, etc. Hundreds of people are killed each year in the U.S. in such work environments. Workers are sometimes struck, pinched, crushed or otherwise harmed while performing their jobs in such environments. Collisions between the various elements at the work sites need to be avoided also to avert property damage.
Referring now to FIG. 1, there is illustrated a simplified example of a work site in which a proximity detection system is implemented. FIG. 1 shows a truck 304 on which a magnetic field generator 81 is mounted. The magnetic field generator 81 generates a magnetic field 92 that surrounds the truck 304. The edge of the magnetic field 92 generated by the magnetic field generator 81 corresponds to the border of a Warning or Danger Zone surrounding the truck 304. A worker 301 within the boundary of the Warning or Danger Zone 92 is in potential danger from being struck or otherwise injured by the truck 304. The worker 301 carries a personal alarm device 60. If the worker 301 and, correspondingly, the personal alarm device 60 are within the magnetic field 92 created by the magnetic field generator 81, the personal alarm device 60 detects the presence of the magnetic field 92 and issues a visual or audio warning. In embodiments of the magnetic field warning system, as detailed in U.S. patent application Ser. No. 11/984,824, which is incorporated herein by reference in its entirety, multiple magnetic filed generators 81 may be used to generate Warning and Danger Zones having a complex shape around the truck 304 or other equipment or areas. These zones may be adjusted in both size and shape. In addition, safe zones may be designated near the truck 304 in which a personal alarm device 60, while within the magnetic field 92, does not generate a warning signal to the worker 301.
FIG. 2 is a diagram of the personal alarm device 60 and the magnetic field generator 81 of the proximity detection system of FIG. 1. A magnetic field generator 80 is contained within a housing 81 and includes an amplifier 84 connected to a ferrite core 90, inductor 86 and capacitor 88. In addition, the magnetic field generator 80 is connected to a power source 83 that provides the power to operate the magnetic field generator 80. The amplifier 84 is connected to and controlled by a controller 82. The ferrite core 90, inductor 86 and capacitor 88 generate a magnetic field 92 in response to an input voltage from the amplifier 84. The amplifier 84 is controlled by the controller 82 which controls the voltage and current outputs of the amplifier 84. The controller 82 is also connected to a receiver 96 and warning system 98. The receiver 96 is connected to an antenna 94 which receives an input signal 76 from a personal alarm device 60. The antenna 94 conveys the signal 76 to the receiver 96 which passes the signal 76 to the controller 82. Upon receiving the signal 76 from the personal alarm device 60, the controller 82 directs the warning system 98 to issue a warning. In one embodiment, the warning system 98 may issue an audio and/or visual warning. In another embodiment, the warning system 98 may be capable of terminating the operation of a vehicle to which the warning system 98 is mounted, for example, the truck 304 of FIG. 1. The magnetic field generator 80 may also be mounted in a location in which it is desirable to warn a worker carrying a personal alarm device 60 of their proximity to the location.
The personal alarm device 60 has x, y, and z axis magnetic field antennas 62 that sense the magnetic field 92 produced by the magnetic field generator 80. The sensed magnetic field signal 80 is passed through filters 66 and an amplifier 68 to a signal detector 64. The signal detector 64 then passes information about the detected signal to a controller 70. The controller 70 activates a transmitter 72 which transmits a corresponding response signal 76 to the magnetic field 92 through an RF antenna 74. In one embodiment, the response signal 76 is an RF signal. The personal alarm device 60 is powered by power source 71. The personal alarm device 60 is carried by the worker 301 (FIG. 1) in order to provide the worker with a warning of their proximity to a magnetic field generator 80.
It has been found however, that existing personal alarm devices have not been worn or used effectively by workers. One issue is that workers are resistant to wearing devices that are bulky, uncomfortable to wear, and are located where they get in the way of the worker's activities. Existing personal alarm devices are typically placed in the pocket or onto a belt of a worker. As such, sounds emitted by the personal alarm devices may not be heard in a noisy environment. Moreover, visual indicators, such as lights, may not be seen by the worker to alert the worker of impending danger. What is needed, is a personal alarm device configured to be worn by a worker such that any signal—audio, visual, or both—transmitted by the personal alarm device will be readily and quickly recognized by the worker. Also needed is a personal alarm device that is miniaturized so as not to be obtrusive or uncomfortable when worn by the worker.